Photoelectric exposure meter with several ranges of measurement



A. BERNHARD ET A1.

' May 28, 1940. 2,202,441

PHOTOELECTRIC EXPOSURE METER WITH SEVERAL RANGES 0F MEASUREMENT.-

Filed NOV.'17, 1937 77. 619W) Mk4 a 63 W sh five/#0; I

9 7710/24 41 v ax terrupted light rays.

be used with the diaphragm in either of these two positions according to the prevailing intensity Patented May 28, 1940 [PATENT ori=|cE.

PHOTOELECTRIC ExrosUnE-MErEn WITH SEVERAL RANGES or MEASUREMENT Albrecht Bernhard and GuidoBeyrich, Nuremberg, Germany, and Manfred Aron, Vienna,

Austria, assi ghors to Metrawatt' Aktiengesellschaft, Fabrik "-.Elektrischer Messg'eraete, Nuremberg, Germany, a German company Application November 17, 1937, Serial No. 175,162

In Germany November 2, 1934 v 5 Claims. (Cl. 8823) It is known to effect a change of the range of measurement in photoelectric, exposure meters by placing a diaphragm in the path of the incident light which limits the amount of light-falling on the photoelectric element in the desired proportions. When on the contrary this diaphragm is removed. from the path of the incident light rays the element is completely exposed to thefunin- The exposure. meter will of light.

The exposure meter is simplified according to this invention due to the fact that 'for the purpose of producing different ranges of measurement, the casing of the exposure meter is provided with two openings for the admission-of the light, which are respectively allotted to the ranges of measurementand admit the incident light to the photoelectric element in proportions corresponding to the two ranges of measurement. The light to be measured is allowed to pass to the element either through one or the other opening according to .the prevailing intensity of light. A suitable construction is obtained by providing a comparatively flat casing and by arranging one opening for the admission of light in thefront of the casing and the other opening in the wider side. Oneor both openings may be made so that they can be closed by a. cover.

Other improvements will be. gathered from the following description in which a construction according to the invention is explained with reference to the accompanying drawing in which:

Figures 1 and 2, show in respective side and front elevations a photoelectric exposure meter according to the invention employing one of the openings for the admission of light.

Figure 3 shows the same exposure meter in side elevation, with the other opening in operation.

In the casing of the exposure meter are mounted a direct current meter 0 and a photoelectric element b electrically connected to it. The 09.5?

ing comprises two openings for the admission of light, the opening 0 in the wide side and the opening d in the front. I 1 4 In the case of low intensity of light, the instrument is used in the position shown in Figures I and 2, in which the light to be measured fallsin the direction of the arrow L through the opening 0 in 'full strength on the photoelectric element b. The opening d may be closed for the measuring period by means of a cap e, but it could also be easily closed by a finger In the case of light of high intensity, the instrument is used in the position shown in Figure 3, in which the light to be measured enters in g the direction of the arrow L through the d. The opening'c may be closed during exposure by means of a cover I rotatably mounted )obliq'uely, so that the latter, when the prevailing light isoi' high intensity will not be illuminated to the same extent as in Figures 1 and 2. As in obliquely from below, which influence the element, it is advisable to provide for reflection of the rays coming-from the top by providing the lowerside g of the light opening 1! with a reflecting, or at least diflusely reflecting surface.

I In the same way, the rays obliquely eomingin from the top may be supplied to the element byproviding the cover f-with a reflecting surface on the inside.

The invention is not limited to the construction described, more particularly, the openings for admission of light may be arranged and formed in. a diflerent way. It is only essential that the light should be supplied to the photoelectric element in different intensities through the two openings, and that the ratio of intensity should correspond to the desired ranges of meas-- urement.

We claim:

1. In a photoelectric exposure meter, a casing, a substantially flat photoelectric element within the casing, a meter connected to the photoelectric element, said casing openings therein of difl'erent areas, one of said openings being arranged with the axis thereof substantially parallel with respect to the flat photoelectric element, the other of said openings being arranged tioned opening being arranged intermediate the photoelectric element and the second mentioned p ing. p

2. In a photoelectric exposure meter, a. casing,

i a substantially flat photoelectric element withinthe casing, a meter connected to the photoelectric element, said casing having an opening therein arranged with the axis thereof substantially parallel with respect to the flat photoelectric element, said casing having another opening therein arranged with the axis thereof substantially perpendicular to the flat photoelectric element, said first mentioned opening arranged inthis case it is mainly the rays of light which come the photoelectric openings therein of 2 termediate the photoelectric element and the second mentioned opening, and reflecting. means for reflecting light entering the casing through the first mentioned opening onto the photoelectric element. a x

- 3. In a photoelectric exposure meter, a casing, a substantially flat photoelectric element within the casing, a meter within the casing connected diflerent sizes, one of said openings being arranged'with the axis thereof substantially parallel with respect to the flat photoelectric element, the other of said openings being arranged with the axis thereof substantially perpendicular .to the photoelectric element, said first mentioned openingsbeing intermediate the photoelectric element and the second mentioned opening, and a cover carried by the casing: for closing one o! the openings.

4. In a photoelectric exposure meter, a casing, a substantially flat photoelectric element within the, casing. meter connected to the photoelectric element, said casing having an opening therein arranged with the axis thereof substantially parallel with respect to the flat photoelectric element, said casing having another opening therein pendicular to the element, said casing having ranged in the end wall of the casing with the openings being arranged with substantially perpendicular to the photoelectric element and in the other side wall of the casing, U

axis thereof substantially parallel with respect to the flat photoelectric element, the other of said the axis thereof and one or said openingsv being larger than that other opening. 1 i

GUIDO BEYRICH. MANFRED ARON.

ALBRECHT BERNHARD. i 

